Generally, conventional automatic transmissions include a torque converter to transfer engine torque from an engine to an input of the transmission, planetary gearsets that provide various gear ratios of torque and thus various drive speeds, and fluid pressure-operated, multi-plate drive or brake clutches and/or brake bands that are connected to the individual elements of the planetary gearsets in order to allow shifts between the various gear ratios
In addition, some conventional automatic transmissions include one-way clutches (i.e., overrunning clutches) that cooperate with the multi-plate clutches to optimize power shift control and include a transmission controller for selectively applying and releasing elements to shift the gears. For example, the controller chooses the proper gear depending on system conditions such as the shift-program selected by the driver (i.e., Drive, Reverse, Neutral, etc.), the accelerator position, the engine condition, and the vehicle speed.
As an accelerator is further depressed, and the vehicle increases speed, the controller disengages appropriate clutches to sequentially shift up through each of the gears until the highest gear is engaged. Specifically, the controller initiates a “single swap” event that releases an engaged clutch and applies an idle clutch such that a shift from a lower gear to a higher gear is accomplished. As can be appreciated, the application and release are preferably controlled and timed such that a driver does not notice or feel the gear shift.
Once the highest gear is engaged, further depression of the accelerator will cause the controller to operate another single swap event such that a lower gear is chosen, and a requisite torque is supplied by the transmission. In this manner, the controller will downshift through the gears, each time applying and releasing a single pair of clutches to perform the requisite gear shift.
Thus, conventional transmissions only use a single applying clutch and a single releasing clutch for each individual shift event. Conventional transmissions do not use a “double swap” event involving more than two clutches to achieve a desired gear ratio. Therefore, while conventional transmissions adequately accomplish gear shifts that meet driving conditions through use of “single swap” events, some conventional transmissions, depending on the gear set arrangements, suffer from the disadvantage of not being able to use desirable and available gear ratios, as the exchange of clutches required to achieve the desired ratio involves more than two clutches. The transmission controls, thus, do not use all available gear ratios and thereby limit the driveability, performance and fuel economy of the transmission.
Therefore, a transmission capable of performing a double swap, to provide a desired gear ratio, is desirable in the industry. Furthermore, a transmission that reduces the requisite number of clutches and gears through use of double swap operations is also desirable.